The present invention relates to a formaldehyde-free flame retardant treatment for cellulose-containing materials, such as cotton or cotton blends (e.g., cotton/polyester and cotton/nylon), which is durable to both laundering and dry cleaning operations.
There are currently several different types of chemical finishes that can be applied to cellulose-containing materials to impart flame retardant (FR) properties. Of these systems, only a few create finished fabrics that can be laundered and dry-cleaned without losing their FR qualities. These treatments are generally referred to as durable FR finishes. Of these finishes, the most pertinent to the current invention are PROBAN and the PYROVATEX brand materials. The PROBAN technology, from Albright & Wilson, is based on the use of tetrakis-(hydroxymethyl)phosphonium chloride ("THPC")--based products and an ammoniation chamber. It is described in detail in the following U.S. Pat. Nos. 4,078,101; 4,145,463) 4,311,855 and 4,494,951, all to Albright and Wilson. The PYROVATEX CP methodology, originally developed by Ciba-Geigy, utilizes dimethyl (N-hydroxymethylcarbamoyl-ethyl)phosphonate or a similar methylol-functional phosphorus-containing analogue as the flame retardant agent. Given the market share that PROBAN and PYROVATEX products control in the industry, it is often difficult to understand the widespread tolerance of the negative aspects associated with the use of these products and the various chemistries they employ.
There have been several versions of the THPC cross-linking chemistry used over the years. For example, the precondensate-NH.sub.3 process (e.g., PROBAN) technology is the most recent of these versions. Although this may be the most durable treatment on the market, this technology involves the use of an ammoniation chamber and strict application conditions to obtain consistent results without significant strength loss to the fabric. In addition to difficult application conditions, the startup costs for implementing this finishing technique and the regulatory issues associated with aimmonia gas make it less than attractive, especially for new arrivals to the market.
In many ways, the PYROVATEX technology suffers from much the same sort of downfalls as the PROBAN technology. Whether it is the original PYROVATEX CP methodology, based on the use of dimethyl (N-hydroxymethylcarbamoyl-ethyl)phosphonate, or other methods using different N-methylol-functional phosphorus-containing analogs, all of the products contain and emit the toxic component formaldehyde (a known carcinogen). In addition to the molecule forming the basis of the PYROVATEX-type approach, a formaldehyde-containing cross-linking resin, such as a N-methylolurea (for example, 1,3-dimethylol-4,5-dihydroxyethyleneurea--"DMDHEU"), N-methylolamide, or N-methylolmelamine, is also required to ensure adequate durability of the chemical finish. These resins are also independently used as durable-press cross-linking agents in the textile industry. The combination of a N-methylol phosphorus-containing analog and a N-methylol cross-linking resin, or the use of either reagent separately, often leads to the release of significant amounts of formaldehyde both during fabric application and throughout the lifetime of the garment. As a result, formaldehyde emission levels are limited and closely regulated throughout the industry. The only reason formaldehyde emissions are still tolerated is due to the lack of an acceptable formaldehyde-free replacement technology.
Given the negative impact of formaldehyde on human health, it has been a primary focus of the cotton apparel and textile finishing industries to create equivalent non-formaldehyde technologies. Accounting for their widespread use, most of the current research effort has been spent on the creation and design of new formaldehyde-free cross-linking agents for cellulose-containing materials. These reagents could be used in many different applications, ranging from use in durable-press finishes to general fixation additives for products such as the PYROVATEX-type FR additives. In the past several years, research efforts have led to the discovery of several new low formaldehyde based systems. These finishes are generally based on the structural modification of DMDHEU, either via substitution or elimination of the pendant methylol functionality. Nevertheless, these new finishing agents have never gained widespread acceptance due to their inadequate performance as cross-linking agents. In general, removal or modification of the most reactive aspect of the DMDHEU molecule has only resulted in the generation of less reactive and less desirable finishing agents.
In addition to modifying DMDHEU, other technologies have also begun to develop. One of the more promising non-formaldehyde systems is based on the use of polycarboxylic acids. These molecules create a cross-linked cellulosic material via the in-situ generation of five-membered cyclic anhydrides and their subsequent reaction with hydroxyl moieties contained within the treated textile. This technology was developed at the United States Department of Agriculture in New Orleans under the direction of Clark Welch and was based on the use of 1,2,3,4-butanetetra-carboxylic acid (BTCA). Representative patents describing this approach are: U.S. Pat. Nos. 4,820,307; 4,936,865; 4,975,209; and 5,221,285.
Since the invention of the BTCA technology, additional investigators have begun to work with polycarboxylic acids to improve their commercial attractiveness. Some of the recent work has focused on the use of polymaleic acid and in some cases citric acid or combinations containing citric acid. Polymaleic acid (PMA) is an inexpensive, commercially available material commonly used as a water treatment chemical. Some aspects of this work are described in PCT International Patent Publication No. WO 98/30387. In addition to PMA, there is a wide range of alternative non-formaldehyde cross-linking resins that can be used in creating durable non-formaldehyde FR treatments for cellulose-containing materials. Many of these resins are currently available and used in the water treatment business for scale-inhibition, some of which even contain small amounts of phosphorus. The utilization of these formaldehyde-free, phosphorus-containing resins may even offer additional advantages over the phosphorus-free cross-linking resins such as PMA. Incorporation of phosphorus species into the cross-linking resin itself may eliminate the need for an external cross-linking catalyst and/or the added phosphorus may result in improved FR properties of the treated cellulose-containing materials. Examples of these resins can be seen in the following U.S. Pat. Nos. 4,046,707; 4,105,551; 4,621,127; 5,376,731; 5,386,038; 5,496,476; 5,705,475; and 5,866,664.